Pairs of the mantis shrimp Gonodactylus festai fought in an open arena. Later, the dominant individual was placed in a cavity and defended it against the subordinate. Visual, tactile, and acoustical displays used during contents for cavities are here described. Fifteen minutes later the subordinate animal was placed in an arena with a cavity containing water from the aquarium of the animal that had just defeated it, water from the aquarium of a stomatopod it had never met, or water that had never contained a stomatopod. Animals readily entered cavities containing clean water, investigated and entered cavities containing strange stomatopod water, and avoided cavities containing water from the home aquarium of the animal that had previously defeated them. © 1979.